Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $51.84   13.448%   $58.8114   $58.81   $58.80   $58.80  
  Purchase #2 $42.76   3.466%   $44.2421   $44.24   $44.25   $44.20  
  Purchase #3 $84.46   13.623%   $95.966   $95.97   $95.95   $96.00  
  Purchase #4 $240.61   4.794%   $252.1448   $252.14   $252.15   $252.10  
  Purchase #5 $143.48   5.277%   $151.0514   $151.05   $151.05   $151.10  
  Purchase #6 $208.48   8.709%   $226.6365   $226.64   $226.65   $226.60  
  Purchase #7 $35.26   6.771%   $37.6475   $37.65   $37.65   $37.60  
  7 purchase totals = $806.89       $866.4997   $866.50   $866.50   $866.40